System and method for handovers in a dual connectivity communications system

ABSTRACT

A method for operating a first access node in a dual connectivity (DuCo) handover includes receiving an event trigger for a combined event from a user equipment (UE), sending to a second access node, a combined instruction for primary secondary cell (PSCell) addition and a role change with the second access node in accordance with the event trigger, adding as the second access node as a PSCell, and indicating to the UE, a role change between the first access node and the second access node.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/655,994, filed on Jul. 21, 2017, which claims the benefit of U.S.Provisional Application No. 62/501,858, filed on May 5, 2017, entitled“System and Method for Handovers in a Dual Connectivity CommunicationsSystem”, which application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a system and method fordigital communications, and, in particular embodiments, to a system andmethod for handovers in a dual connectivity (DuCo) communicationssystem.

BACKGROUND

Handovers support device mobility by allowing the device to changeconnectivity from a first access node to a second access node. Ahandover typically occurs when the device moves out of service of thefirst access node into service of the second access node. Withouthandovers, the quality of the connection between the device and thefirst access node will deteriorate until the connection is broken.

SUMMARY

Example embodiments provide a system and method for handovers in a dualconnectivity (DuCo) communications system.

In accordance with an example embodiment, a method for operating a firstaccess node in a DuCo handover is provided. The method includesreceiving, by the first access node, an event trigger for a combinedevent from a user equipment (UE), sending, by the first access node, toa second access node, a combined instruction for primary secondary cell(PSCell) addition and a role change with the second access node inaccordance with the event trigger, adding, by the first access node, asthe second access node as a PSCell, and indicating, by the first accessnode, to the UE, a role change between the first access node and thesecond access node.

Optionally, in any of the preceding embodiments, the method furthercomprises receiving, by the first access node, a UE context releaseinstruction from the second access node, and releasing, by the firstaccess node, a UE context associated with the UE.

Optionally, in any of the preceding embodiments, the method furthercomprises forwarding, by the first access node, at least one data packetto the second access node prior to receiving the UE context releaseinstruction.

Optionally, in any of the preceding embodiments, the method furthercomprises receiving, by the first access node, an acknowledgement forboth the PSCell addition and the role change from the second accessnode.

Optionally, in any of the preceding embodiments, wherein the eventtrigger reflects a combination of a first quality indicator associatedwith the first access node falling below a first threshold and a secondquality indicator associated with the second access node rising above asecond threshold relative to a third quality indicator associated withthe first access node.

In accordance with an example embodiment, a method for operating a firstaccess node in a DuCo handover is provided. The method includesreceiving, by the first access node, a combined event trigger for acombined event from a UE, sending, by the first access node, to a secondaccess node, a combined instruction for a role change with the secondaccess node and a PSCell release in accordance with the combined eventtrigger, indicating, by the first access node, to the UE, a role changebetween the first access node and the second access node, receiving, bythe first access node, a UE context release instruction from the secondaccess node, and releasing, by the first access node, a UE contextassociated with the UE.

Optionally, in any of the preceding embodiments, the method furthercomprises forwarding, by the first access node, at least one data packetto the second access node prior to receiving the UE context releaseinstruction.

Optionally, in any of the preceding embodiments, the method furthercomprises receiving, by the first access node, an event trigger for aPSCell addition, and adding, by the first access node, the second accessnode as a PSCell in accordance with the event trigger.

Optionally, in any of the preceding embodiments, wherein receiving theevent trigger and adding the second access node occur prior to receivingthe combined event trigger.

Optionally, in any of the preceding embodiments, wherein the combinedevent trigger reflects a combination of a first quality indicatorassociated with the first access node falling below a first thresholdand a second quality indicator associated with the second access noderising above a second threshold relative to a third quality indicatorassociated with the first access node.

In accordance with an example embodiment, a method for operating asecond access node in a DuCo handover is provided. The method includesreceiving, by the second access node, from a first access node, acombined instruction for a role change with the second access node and aPSCell release, changing, by the second access node, to operating as aprimary cell (PCell), and sending, by the second access node, a UEcontext release instruction to the first access node.

Optionally, in any of the preceding embodiments, the method furthercomprises establishing, by the second access node, a UE context for a UEas a PSCell.

Optionally, in any of the preceding embodiments, the method furthercomprises operating, by the second access node, as a PSCell prior tosending the UE context release instruction.

In accordance with an example embodiment, a method for processingpackets during a role change between a first access node and a secondaccess node is provided. The method includes applying, by a UE, to afirst set of packets, a first set of packet data convergence protocol(PDCP) functions associated with the first access node prior to aprocessing of a switch indicator, wherein the first set of PDCPfunctions associated with the first access node includes sequence numberassignment and header compression, applying, by the UE, to a second setof packets, a first set of PDCP functions associated with the secondaccess node after the processing of the switch indicator, wherein thefirst set of PDCP functions associated with the second access nodeincludes sequence number assignment and header compression, applying, bythe UE, to a third set of packets, a second set of PDCP functionsassociated with the first access node when communicating with the firstaccess node, wherein the second set of PDCP functions associated withthe first access node includes header addition and/or removal anddeciphering and/or ciphering, and applying, by the UE, to a fourth setof packets, a second set of PDCP functions associated with the secondaccess node when communicating with the second access node, wherein thesecond set of PDCP functions associated with the second access nodeincludes header addition and/or removal and deciphering and/orciphering.

Optionally, in any of the preceding embodiments, wherein the switchindicator is an activation time, and wherein applying the second set ofPDCP functions associated with the first access node and applying thesecond set of PDCP functions associated with the second access nodeoccur both prior to and subsequent to the activation time.

Optionally, in any of the preceding embodiments, wherein the activationtime comprises a time when the role change occurs.

Optionally, in any of the preceding embodiments, wherein the first setof packets comprises packets exchanged prior to the activation time, andwherein the third set of packets comprises packets exchanged with thefirst access node.

Optionally, in any of the preceding embodiments, wherein the second setof packets comprises packets exchanged after the activation time, andwherein the fourth set of packets comprises packets exchanged with thesecond access node.

Optionally, in any of the preceding embodiments, wherein the switchindicator is a PDCP protocol data unit (PDU) indicating the role change,and wherein applying the second set of PDCP functions associated withthe first access node and applying the second set of PDCP functionsassociated with the second access node occur both prior to andsubsequent to the processing of the PDCP PDU.

Optionally, in any of the preceding embodiments, wherein the first setof packets comprises packets exchanged prior to the processing of thePDCP PDU, and wherein the third set of packets comprises packetsexchanged with the first access node.

Optionally, in any of the preceding embodiments, wherein the second setof packets comprises packets exchanged after the processing of the PDCPPDU, and wherein the fourth set of packets comprises packets exchangedwith the second access node.

Optionally, in any of the preceding embodiments, wherein the PDCP PDU isone of a PDCP control PDU indicating the role change or a PDCP data PDUincluding an end marker.

Practice of the foregoing embodiments enables an optimization ofhandovers in a dual connectivity communications system by combining aswitching of primary and secondary node roles with either the additionof a target node as a secondary node or the release of the formerprimary node. The optimization reduces the amount of signaling andnumber of procedural steps, which helps to improve overall handoverperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an example wireless communications system accordingto example embodiments described herein;

FIG. 2 illustrates a flow diagram of operations occurring in a 3GPP DuCohandover procedure;

FIG. 3A illustrates a flow diagram of example operations occurring in atwo-step DuCo handover where the role change is combined with theaddition of the PSCell according to example embodiments describedherein;

FIG. 3B illustrates a flow diagram of example operations occurring in atwo-step DuCo handover where the role change is combined with the PSCellrelease according to example embodiments described herein;

FIG. 4 illustrates a diagram of transmissions occurring at devices inaccordance with the first example embodiment described herein;

FIG. 5 illustrates a diagram of processing performed by andtransmissions made by devices participating in a two-step DuCo handoverwith a combined PSCell addition and role change according to exampleembodiments described herein;

FIG. 6 illustrates a diagram of transmissions occurring at devices inaccordance with the second example embodiment described herein;

FIG. 7 illustrates a diagram of processing performed by andtransmissions made by devices participating in a two-step DuCo handoverwith a combined role change and PSCell release according to exampleembodiments described herein;

FIG. 8A illustrates a sublayer view of devices participating in a rolechange phase of a two-step DuCo handover according to exampleembodiments described herein;

FIG. 8B illustrates a logical view of access nodes participating in arole change phase of a two-step DuCo handover as presented in FIG. 8Aaccording to example embodiments described herein;

FIG. 8C illustrates a logical view of access nodes participating in arole change phase of a two-step DuCo handover where the source nodeperforms the PDCP functions according to example embodiments describedherein;

FIG. 8D illustrates a logical view of access nodes participating in arole change phase of a two-step DuCo handover where the source nodeperforms the upper PDCP functions according to example embodimentsdescribed herein;

FIG. 9A illustrates a flow diagram of example operations occurring in asource node participating in a two-step DuCo handover according to thefirst example embodiment described herein;

FIG. 9B illustrates a flow diagram of example operations occurring in atarget node participating in a two-step DuCo handover according to thefirst example embodiment described herein;

FIG. 10A illustrates a flow diagram of example operations occurring in asource node participating in a two-step DuCo handover according to thesecond example embodiment described herein;

FIG. 10B illustrates a flow diagram of example operations occurring in atarget node participating in a two-step DuCo handover according to thesecond example embodiment described herein;

FIG. 11 illustrates a flow diagram of example operations occurring in alayered PDCP entity of a UE processing received packets during a rolechange of a DuCo handover according to example embodiments describedherein;

FIG. 12 illustrates a flow diagram of example operations occurring in adevice processing PDCP packets according to example embodimentsdescribed herein;

FIG. 13 illustrates an example communication system according to exampleembodiments described herein;

FIGS. 14A and 14B illustrate example devices that may implement themethods and teachings according to this disclosure; and

FIG. 15 is a block diagram of a computing system that may be used forimplementing the devices and methods disclosed herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently example embodiments are discussedin detail below. It should be appreciated, however, that the presentdisclosure provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the embodiments, and do not limit the scope of the disclosure.

FIG. 1 illustrates an example wireless communications system 100. Asshown in FIG. 1, communications system 100 supports dual connectivity(DuCo) operation where a single user equipment (UE) can be connected totwo or more access nodes, and simultaneously exchange data with the twoor more access nodes. The two or more access nodes may be part of thesame network infrastructure or different network infrastructures (as anexample, in a two access node situation, a first access node may be partof a legacy macrocell network and a second access node may be part of amanaged or unmanaged overlay picocell network).

Communications system 100 includes access nodes, such as access node 105and access node 107. The access nodes serve a plurality of UEs, such asUE 110, UE 112, and UE 114. While it is understood that communicationssystems may employ multiple access nodes capable of communicating with anumber of UEs, only two access nodes and a number of UEs are illustratedfor simplicity. Access nodes are also commonly referred to as NodeBs,evolved NodeBs (eNBs), next generation (NG) NodeBs (gNBs), master eNBs(MeNBs), secondary eNBs (SeNBs), master gNBs (MgNBs), secondary gNBs(SgNBs), base stations, access points, remote radio heads, and so on.Access nodes may be used as a more general term for eNBs, gNBs, NodeBs,MeNBs, SeNBs, MgNBs, SgNBs, base stations, access points, remote radioheads, and so on. Similarly, UEs are also commonly referred to asmobiles, mobile stations, stations, terminals, subscribers, users, andthe like.

As shown in FIG. 1, UE no is mobile. Initially, UE no is connected withaccess node 105, which is serving as a source node for UE 110. As UE nomoves about, UE no moves into an area where UE no is able to connect toboth access node 105 and access node 107. When UE no is connected toboth access node 105 and access node 107, UE no is referred to as UE 120to reduce confusion. As UE no continues to move above, UE no moves to anarea where UE no is able to connect to only access node 107. When UE nois connected to access node 107, UE no is referred to as UE 125 toreduce confusion.

As UE no moves about, UE no participates in a DuCo handover, which is atechnique used to avoid data interruption. UE no is initially connectedto access node 105, which serves as a primary node for UE 110. As UE nomoves towards access node 107, a DuCo handover is initiated. The DuCohandover involves the addition of access node 107 as a secondary node ofUE 110 (shown in FIG. 1 as UE 120 at the point of the DuCo handover).After the addition of access node 107 as a secondary node of UE 110,access node 105 is serving as the primary node and access node 107 isserving as the secondary node. The DuCo handover also involves a rolechange, where the primary node of UE 120 (access node 105 prior to therole change) becomes the secondary node of UE 120 and the secondary nodeof UE 120 (access node 107 prior to the role change) becomes the primarynode of UE 120. After the role change, access node 107 is serving as theprimary node and access node 105 is serving as the secondary node. TheDuCo handover completes with the release of the secondary node (accessnode 105). After the release of the secondary node, UE 125 is onlyserved by access node 107.

The DuCo handover prevents data interruption, in the sense that the UEalways has an active data path to and/or from the network, through atleast one of the access nodes. During middle portion of the DuCohandover, while both source and target nodes are active, data may betransmitted to the UE in two independent streams or duplicated over thetwo connections present during the DuCo handover.

If the two connections share a common frequency band, coordination oftransmissions over the two connections is used to avoid potentialinterference. Depending upon the capabilities of the UE, a variety oftechniques may be used to avoid interference, including:

-   -   A dual radio UE can communicate on the two connections        simultaneously with interference control occurring in the        frequency domain.    -   A single radio UE communicates using interference control in the        time domain, by time division multiplexing (TDM) of the two        connections, for example.    -   It is noted that interference coordination if the access nodes        are not synchronous may require additional techniques, e.g.,        guard times are used to compensate for frame and/or subframe        boundary misalignment.

FIG. 2 illustrates a flow diagram of operations 200 occurring in a 3GPPDuCo handover procedure. Operations 200 begin with the addition of atarget node as a secondary node (block 205). The target node is added asa primary secondary cell (PSCell) to trigger DuCo operation togetherwith the source node. A role change of primary and secondary nodesoccurs (block 210). The roles of the source node and the target node areswitched in terms of primary cell (PCell) and PSCell. The secondary nodeis released (block 215), where the PSCell (the source node, which wasthe primary node prior to the role change) is released.

The 3GPP DuCo handover procedure improves the robustness of the handoverprocess because the UE does not depend upon a single connection duringthe critical handover period. No additional interruption time isexpected following completion of the 3GPP DuCo handover. However, thethree steps involved in the 3GPP DuCo handover is longer than a normalhandover and requires additional control signaling compared to a normalhandover, thereby increasing the risk for a radio link failure (RLF)and/or a handover failure (HOF).

The flow diagram for the 3GPP DuCo handover shows that the 3GPP DuCohandover is sub-optimal. There are a number of events that need to occurindependently to trigger the addition of the PSCell, the role change,and the PSCell release. Each of the steps has its own signaling and mayneed to have its own measurement triggering conditions. This comparesunfavorably to a 3GPP LTE handover, which is a one-step processinvolving a handover request and handover response. The complexityassociated with the DuCo handover results in high handover latency, eventhough there are no periods of data interruption.

Furthermore, more signaling also means increased vulnerability to lostmessages. However, a lost message should not result in a call dropbecause the point of DuCo operation is that the UE has two connectionsand can keep using the connection that did not fail. But the lostmessage may result in a failed handover, e.g., leaving the UE stillserved by the original source node contrary to the intent of the DuCohandover. In some scenarios, the source node may fail quickly, leavingthe UE with the need to recover on the target node while the target nodeis still the PSCell (prior to the occurrence of the role change).Therefore, there is a need for a system and method for a DuCo handoverwith optimized flow, reduced signaling, and fewer procedural steps.

According to an example embodiment, a DuCo handover with two steps ispresented. The three-step 3GPP DuCo handover is optimized into atwo-step DuCo handover procedure. The three-step procedure is optimizedby combining the role change with one of the other two steps (either theaddition of the PSCell or the PSCell release), producing the two-stepDuCo handover procedure. The two-step DuCo handover procedure comprisesa combined step and one single step. It is noted that until the PSCellis released, data can be sent to the UE on both connections of the DuCoconfiguration. Management of measurement events triggering the newcombined step is presented below.

According to a first example embodiment, the role change is combinedwith the addition of the PSCell. According to a second exampleembodiment, the role change is combined with the PSCell release. Ineither example embodiment, the combined step can be triggered by asingle measurement event. The measurement event reflects the combinedconditions that enable the addition and/or release with the role change.Measurement behavior needed to enable the example embodiments arepresented below. User plane handling (e.g., routing of data from thecore network (CN) to the access nodes) needs to switch when the rolechange occurs, and packet forwarding is considered to ensure that theDuCo handover remains lossless.

FIG. 3A illustrates a flow diagram of example operations 300 occurringin a two-step DuCo handover where the role change is combined with theaddition of the PSCell. The two-step DuCo handover comprises theaddition of a target node as a secondary node (i.e., the PSCell) (block305) and the role change (block 310) into a combined step (blocks 315).The two-step DuCo handover also comprises the release of the PSCell(block 320).

FIG. 3B illustrates a flow diagram of example operations 350 occurringin a two-step DuCo handover where the role change is combined with thePSCell release. The two-step DuCo handover comprises the addition of atarget node as a secondary node (i.e., the PSCell) (block 355). Thetwo-step DuCo handover also includes the role change (block 360)combined with release of the PSCell (block 365) into a combined step(blocks 370).

FIG. 4 illustrates a diagram 400 of transmissions occurring at devicesin accordance with the first example embodiment. Diagram 400 illustratestransmissions occurring at a UE 405, a source node 407, and a targetnode 409, as the devices participate in a two-step DuCo handover inaccordance with the first example embodiment. It is noted that diagram400 presents a high-level view of the first example embodiment and omitssome transmissions.

UE 405 transmits a first measurement report to source node 407 (event415). The first measurement report is an event trigger for the combinedevent (the combined role change and addition of the PSCell event).Source node 407 sends a request message for the combined event to targetnode 409 (event 417). Target node 409 sends an acknowledgement messageto the request for the combined event to source node 407 (event 419). UE405 optionally transmits a second measurement report to target node 409(event 421). Event 421 (the second measurement report) is optional iftarget node 409 can decide autonomously to complete the two-step DuCohandover based on event 417. The second measurement report is an eventtrigger for the PSCell release event. Target node 409 transmits a PSCellrelease request to source node 407 (event 423). It is noted thatalthough the second measurement report is optional, the resultinghandover is still not a single step handover because the addition of thePSCell and the role change need to be completed and acknowledged beforethe PSCell release can take place, meaning that the PSCell releaseremains a separate event.

The event trigger for the combined event (the first measurement reportof event 415) reflects two conditions: the source node is degrading(hence the handover is needed) and a neighbor node (the target node) isstrong enough to be a PSCell candidate. In 3GPP LTE, there are twoseparate measurement events: event A2 (indicating that serving nodebecomes worse than a threshold) and event A3 (indicating that neighbornode becomes an offset better than PCell and/or PSCell). Event M is aclose combination that indicates that PCell and/or PSCell have becomeworse than a first threshold (threshold1) and that neighbor node hasbecome better than a second threshold (threshold2). However, event Mdoes not capture the relationship between the PCell and/or PSCell andthe neighbor node as does event A3.

According to an example embodiment, a new event indicating that servingnode has become worse than a threshold and that a neighbor node hasbecome an offset better than PCell and/or PSCell is provided. It isnoted that the new event is not equivalent to neighbor node has becomebetter than a threshold plus an offset, because if the serving node hasquickly become significantly worse than the threshold, the trigger levelfor the target node is correspondingly lower than the threshold plus theoffset. The new event provides for the correct behavior because if theserving node quality drops quickly, the requirement of a target node ofsufficient quality (a good enough target node) is correspondinglylooser. In other words, the network is more willing to use a target nodeto let the UE recover from the rapid degradation of the serving node.The offset from the PCell and the neighbor node should be small intypical conditions (the offset should be positive however, as opposed tothe offset of event A3, which may be negative).

Network handling of the new event may be to trigger the combined eventof the addition of the PSCell and the role change.

FIG. 5 illustrates a diagram 500 of processing performed by andtransmissions made by devices participating in a two-step DuCo handoverwith a combined PSCell addition and role change. Diagram 500 illustratesprocessing performed by and transmissions made by a UE 505, a sourcenode 507, and a target node 509, as the devices participate in atwo-step DuCo handover with a combined PSCell addition and role change.

Source node 507 receives data intended for UE 505 from the core network(event 515). Source node 507 forwards data received from the corenetwork to UE 505 (event 517). UE 505 transmits a measurement report tosource node 507 (event 519). The measurement report is an event triggerfor the combined PSCell addition and role change event. Source node 507sends message including a combined PSCell addition request and a rolechange indication to target node 509 (event 521). Target node 509 isidentified in the measurement report and is a neighbor node that meetsthe conditions of the event. Target node 509 sends a combined PSCelladdition and role change acknowledge message to source node 507 (event523). UE 505 and source node 507 exchange transmissions in areconfiguration procedure (event 525). One of the transmissionsexchanged between UE 505 and source node 507 serves as an indicator ofthe role change at source node 507 and target node 509. Source node 507sends a combined PSCell addition and role change complete message totarget node 509 (event 527). Source node 507 forwards data intended forUE 505 to target node 509 (event 529). The data forwarded by source node507 includes data that source node 507 has received from the corenetwork but source node 507 has not had the opportunity to transmit toUE 505 before the combined PSCell addition and role change completed.

UE 505 and target node 509 participate in a random access procedure(event 531). The random access procedure is commonly referred to as aRACH procedure. The random access procedure establishes a connectionbetween UE 505 and target node 509. The transmission of a random accessresource by UE 505 to target node 509 may be an event trigger initiatingthe PSCell release. Source node 505 sends a path update to the corenetwork (event 533). The path update may alternatively serve as anindicator of the role change at source node 507 and target node 509. Thepath update informs the core network that target node 509 is now thePCell of UE 505.

After the path update has occurred, target node 509 receives dataintended for UE 505 from the core network (event 535). Target node 509forwards data received from the core network and source node 507 to UE505 (event 537). Because a connection between source node 507 and UE 505is still available, the connection may be exploited to improvecommunications performance. Target node 509 sends data intended for UE505 to source node 507 (event 539). The data sent by target node 509 tosource node 507 may be formatted and routed in accordance with a splitbearer configuration. Source node 507 forwards the data to UE 505 (event541). It is noted that at some point, the connection between source node507 and UE 505 will be discarded when source node 507 is released fromoperating as PSCell. The releasing of source node 507 from operating asPSCell may involve the release of the context of UE 505 from source node507. In other words, the UE context of UE 505 is released from sourcenode 507. Source node 507 may receive an instruction from target node509 to release the UE context of UE 505.

As shown in FIG. 5, the PSCell addition and the role change occurtogether and are acknowledged together. Therefore, there is no datadelivered through target node 509 when it is operating as a PSCell. Datadelivery through the target node begins after the path update, event533. After the path update, no additional data comes to UE 505 fromsource node 507 until target node 509 begins to deliver data to sourcenode 507 after target node 509 begins operating as PCell. It is notedthat the amount of time that source node 507 is not delivering datashould be short. The delivery of data by source node 507 may continueuntil a second event resulting in the release of source node 507 asPSCell completes.

FIG. 6 illustrates a diagram 600 of transmissions occurring at devicesin accordance with the second example embodiment. Diagram 600illustrates transmissions occurring at a UE 605, a source node 607, anda target node 609, as the devices participate in a two-step DuCohandover in accordance with the second example embodiment. It is notedthat diagram 600 presents a high-level view of the second exampleembodiment and omits some transmissions.

UE 605 transmits a first measurement report to source node 607 (event615). The first measurement report is an event trigger for the additionof the PSCell. Source node 607 sends a PSCell addition request messageto target node 609 (event 617). Target node 609 sends a PSCell additionacknowledgement message to source node 607 (event 619). Source node 607sends a path update to the core network (event 621).

UE 605 transmits a second measurement report to source node 607 (event623). The second measurement report is an event trigger for a combinedevent (the combined role change and PSCell release event). Source node607 sends a role change and PSCell release request message to targetnode 609 (event 625). Target node 609 sends a message including a rolechange acknowledge and PSCell release indication to source node 607(event 627). Source node 607 sends a path update to the core network(event 629).

According to the second example embodiment, both measurement reports,events 615 and 623, are necessary because the radio conditionstriggering the release of source node 607 are separate from theconditions reported to trigger the addition of the PSCell. It is notedthat the conditions associated with event 615 should be relaxed toprevent a situation where the quality of source node 607 crashes beforethe path update is delivered to the core network, event 621.

In the second example embodiment, the PSCell addition proceeds asnormal, so packets are delivered through source node 607 operating asthe PCell and target node 609 operating as the PSCell, as in 3GPP LTE.Hence, simultaneous data transmission over the two connections may occuruntil event A3 is triggered by second measurement report, event 623.

At event A3, source node 607 triggers the role change and the PSCellrelease, and stops operating as the PCell. If the PSCell release isexecuted immediately, no data is delivered through source node 607during its brief lifetime as PSCell. Any data that arrives at sourcenode 607 from the core network while source node 607 is operating asPSCell is forwarded to target node 609 (which is now operating asPCell).

Alternatively, the PSCell release may be delayed until after the pathswitch (path update, event 629) to allow simultaneous delivery tocontinue for a short time after the role change. In such a situation,data would arrive at target node 609 (operating as PCell) and will beforwarded to source node 607 (operating as PSCell) in accordance withlegacy operation. There remains no separate triggering event for thePCell release in this alternative so from the technical standards pointof view it remains a two-step handover procedure. A decision on when tostop simultaneous delivery may be up to the network implementation oftarget node 609.

FIG. 7 illustrates a diagram 700 of processing performed by andtransmissions made by devices participating in a two-step DuCo handoverwith a combined role change and PSCell release. Diagram 700 illustratesprocessing performed by and transmissions made by a UE 705, a sourcenode 707, and a target node 709, as the devices participate in atwo-step DuCo handover with a combined role change and PSCell release.

Source node 707 receives data intended for UE 705 from the core network(event 715). Source node 707 forwards data received from the corenetwork to UE 705 (event 717). UE 705 transmits a first measurementreport to source node 707 (event 719). The first measurement report isan event trigger for the PSCell addition event. Source node 707 sends aPSCell addition request message to target node 709 (event 721). Targetnode 709 is identified in the measurement report and is a neighbor nodethat meets the conditions of the event. Target node 709 sends a PSCelladdition acknowledgement message to source node 707 (event 723). Sourcenode 707 sends a PSCell addition complete message to target node 709(event 725).

UE 705 and target node 709 participate in a random access procedure(event 727). The random access procedure establishes a connectionbetween UE 705 and target node 709. Source node 707 optionally sends apath switch request to the core network (event 729). Source node 707,operating as PCell, sends data to UE 705 (event 731) and forwards datafor UE 705 to target node 709 (event 733). The data forwarded fromsource node 707 to target node 709 may be formatted and routed inaccordance with a split bearer configuration. Target node 709 may alsoreceive data intended for UE 705 from the core network (event 735).Target node 709, operating as PSCell, forwards data to UE 705 (event737).

UE 705 transmits a second measurement report to source node 707 (event739). The second measurement report is an event trigger for the combinedrole change and PSCell release event. Source node 707 sends a rolechange and PSCell release request message to target node 709 (event741). Target node 709 sends message including a role changeacknowledgement and a PSCell release indication to source node 707(event 743). Source node 707, operating as PCell, forwards any remainingdata to UE 705 (event 745) and forwards the data to target node 709(event 747).

Source node 707 and UE 705 participate in a reconfiguration procedure byexchanging transmissions (event 749). One of the transmissions exchangedbetween UE 705 and source node 707 serves as an indicator of the rolechange at source node 707 and target node 709. The reconfigurationprocedure ends the over the air (OTA) data transmission from source node707. Any further data received from the core network is forwarded totarget node 709 as packet data convergence protocol (PDCP) protocol dataunits (PDUs) to be delivered on a radio bearer of target node 709.Source node 707 sends a path update to the core network (event 751). Thepath update starts delivery of data from the core network to target node709 (operating as PCell). The path update may alternatively serve as anindicator of the role change at source node 707 and target node 709.Target node 709, operating as PCell, forwards data to UE 705 (event753).

It is noted that from events 727 to 749, packets can be duplicated OTA.In other words, UE 705 may receive the same data from both source node707 and target node 709 to ensure data continuity is maintained.

An optional path switch request, event 729, is applicable in thesituation where the core network immediately sets up a secondary cellgroup (SCG) bearer. The early path switch request takes the earliestpossible opportunity to deliver data from the core network throughtarget node 709. It is reasonable for the core network to prefer datadelivery through target node 709 because target node 709 is expected topresent a better quality link in the near future, while the link throughsource node 707 is potentially failing. Although SCG bearer is not arequired behavior, it may be reasonable to set it up at this point.

According to an example embodiment, during a role change, a UE and thenetwork are able to process packets according to a split betweensublayers of the PDCP layer. This results in the UE operating with adual PDCP entity, with certain functions that are different between thePCell and the PSCell. In the split bearer, the source node (operating asPCell) may handle PDCP sequence number assignment and robust headercompression (RoHC), before passing the packet to the target node(operating as PSCell), in the downlink direction; the target node maythen handle ciphering and header addition. For the uplink direction, thetarget node handles deciphering and header removal before passing thepacket to the source node for upper sublayers of the PDCP layer, wherethe source node handles header decompression and PDCP sequence numbermanagement. Alternatively, during a role change, a UE and the networkare able to process packets according to a split between the PDCP layerand the RLC layer. This results in the UE operating with a single PDCPentity. In the split bearer scenario, the source node (operating asPCell) may handle all of the PDCP functions including sequence numberassignment, RoHC, and packet ciphering, before passing the packet (PDCPPDU) to the target node (operating as PSCell), in the downlinkdirection; the target node may then deliver the PDCP PDU to the RLClayer for OTA transmission. For the uplink direction, the target nodehandles RLC layer functions before passing the packet to the source nodefor PDCP layer, where the source node handles deciphering, headerdecompression, PDCP sequence number management and packet reordering.The following description of FIG. 8A focuses on the case where UEoperates with a dual PDCP entity.

FIG. 8A illustrates a sublayer view of devices 800 participating in arole change phase of a two-step DuCo handover. Shown in FIG. 8A aresublayer views of a PCell 805, a PSCell 807, and a UE 809. PCell 805includes a PDCP entity 815 with a sequence number (SN)numbering/reordering unit 817, a header compression/decompression unit819, a ciphering/deciphering unit 821, and a header adding/removing unit823. PCell 805 also includes a radio link control (RLC) entity 825, amedium access control (MAC) entity 827, and a physical (PHY) layerentity 829. PSCell 807 also features a similar structure.

UE 809 includes dual PDCP entities 835 and 837, with one PDCP entity forPCell 805 and one PDCP entity for PSCell 807. The dual PDCP entities caninclude separate SN numbering/reordering unit and RoHC (headercompression/decompression) unit within each PDCP, or include a common SNnumbering/reordering unit 839 and a common headercompression/decompression unit 841 to process packets for communicationwith PCell 805 and PSCell 807. Each of the dual PDCP entities alsoincludes a ciphering/deciphering unit and a header adding/removing unit,for processing packets for communication with either of PCell 805 andPSCell 807. UE 809 further includes dual RLC, MAC, and PHY entities. Asan illustrative example, UE 809 uses PHY entity 851, MAC entity 849, RLCentity 847, header adding/removing unit 845, and ciphering/decipheringunit 843 to process packets received from PCell. Deciphered packets maybe provided to common SN numbering/reordering unit 839 and common headercompression/decompression unit 841, along with deciphered packets fromPSCell 807 (after processing by corresponding entities and units of UE809).

The two ciphering/deciphering units at UE 809 reduce the interruption ofreset or reconfiguration, by having a separate ciphering/decipheringunit dedicated to each one of PCell 805 and PSCell 807. The differentunits and entities of PCell 805, PSCell 807, and UE 809 synchronize asthe role change between PCell 805 and PSCell 807 takes place.

When PCell 805 and PSCell 807 change roles, upper PDCP functions (i.e.,SN reordering unit and header compression/decompression unit) need to bereset, but lower PDCP functions (i.e., ciphering/deciphering unit andheader adding/removing unit) may be maintained because they areindependent of the roles served by the access nodes (e.g., PCell orPSCell) that transmitted the packets.

UE 809 uses ciphering/deciphering unit 843 when communicating OTA withPCell 805 before or after the role change, and correspondingciphering/deciphering unit when communicating OTA with PSCell 807.However, at the role change, UE 809 switches which set of upper PDCPfunctions is used for PCell 805 and PSCell 807. If the switch does nottake place, there is a risk that, for example, an uplink packet isprocessed for PCell 805 (header compression/decompression unit 841) butis delivered to PSCell 807 (now operating as a PCell) OTA, just afterthe role change, and passed on to the upper PDCP functions (SNreordering unit and header compression/decompression unit) of PSCell807.

According to an example embodiment, the switching process can becontrolled by a PDCP layer control PDU. As an example, the PDCP entityof the source cell may send a specific PDCP control PDU to the UE toindicate the switching. Alternatively, an end marker can be put into theheader of the last PDCP PDU sent by the source node to indicate theswitching. In this case, the end marker indicates to the UE the SNboundary for the switching. The PDCP PDU with a SN larger than the SN ofthe PDCP PDU carrying the end marker will be transmitted by the targetnode. As an additional alternative, the switching process can besynchronized by aligning on a particular system frame number (SFN) orsome other time marker of the switch. When the UE is reconfigured forthe role change, the UE is given an activation time, i.e., an indicationof an instant at which the role change will take place. Therefore, thePDCP layer control PDU, the end marker present in a PDCP PDU, theactivation time, or some other indicator usable in marking the switchmay be referred to as a switch indicator. The abovementioned switchingprocess is described for the downlink, where the network controls theswitching process for downlink, and when the UE receives the switchingindicator, the UE will act accordingly for a subsequent uplinktransmission. Therefore, transmissions in both downlink and uplink canbe switched. As an additional alternative, the UE can signal the networkvia the similar methods described above (i.e., PDCP layer control PDU,the end marker present in a PDCP PDU, the activation time, or some otherindicator usable in marking the switch) to inform the network of theswitching process for uplink transmission and the network can actaccordingly for a subsequent downlink transmission. Furthermore, the UEand the network can signal the uplink switching process and downlinkswitching process separately, i.e., the UE indicates the uplinkswitching to the network and the network indicates the downlinkswitching to the UE.

With respect to the split bearer, packet processing before theactivation time uses the upper PDCP functions of PDCP entity 815 ofPCell 805. Packet processing after the activation time uses the upperPDCP functions of the PDCP entity of PSCell 807.

The selection of which lower PDCP functions to use is based on whichnode (source node or target node) the UE is communicating with OTA,independent of which one is the PCell or the PSCell.

With respect to duplicate packets, duplicate detection in PDCP has beenperformed at the PDU level. However, because the SN is assigned toservice data units (SDUs) in the upper PDCP functions, a single SDU maybe processed into two different PDCP PDUs by the lower PDCP functions ofthe two different PDCP entities. Thus cases may occur in which an SDU istransmitted once through PCell 805 and once through PSCell 807, but theresulting PDUs cannot be recognized as duplicates by the receivingentity. That is, the existing methods of PDCP duplicate detection canfail in this sublayered PDCP design.

According to an example embodiment, the PDCP entities perform duplicatedetection at the SDU level. In other words, a receiving PDCP entityfirst processes the PDUs and when a SDU is generated, the receiving PDCPentity checks the SN against those of previously received SDUs.

FIG. 8B illustrates a logical view of access nodes 860 participating ina role change phase of a two-step DuCo handover as presented in FIG. 8A.Upper PDCP functions (such as sequence numbering 862, and RoHC 863) areperformed by a single PDCP entity 861, such as at the source nodeoperating as a PCell, while lower PDCP functions (such asciphering/deciphering, and header adding/removing), as well as RLC andMAC entities are performed separately by lower PDCP entities 864 and 865at the source node and the target node.

FIG. 8C illustrates a logical view of access nodes 870 participating ina role change phase of a two-step DuCo handover where the source nodeperforms the PDCP functions. As shown in FIG. 8C, source node 872(operating as PCell) provides PDCP processing (by PDCP entity 876, forexample) for downlink packets before passing at least some of theprocessed packets to target node 874 (operating as PSCell). PDCP entity876 may include sequence numbering and reordering 877, headerdecompression 878, deciphering 879, and header removing 880.

FIG. 8D illustrates a logical view of access nodes 885 participating ina role change phase of a two-step DuCo handover where the source nodeperforms the upper PDCP functions. As shown in FIG. 8D, source node 887(operating as PCell) provides upper PDCP processing (by upper PDCPentity 888, for example) for downlink packets before passing at leastsome of the processed packets to target node 889 (operating as PSCell).Source node 887 and target node 889 provide lower PDCP processing (bylower PDCP entity 890 of source node 887 and lower PDCP entity 891 oftarget node 889, for example) for their respective processed packets.PDCP entity of target node 889 may be operating as a slave PDCP entity.

FIG. 9A illustrates a flow diagram of example operations 900 occurringin a source node participating in a two-step DuCo handover according tothe first example embodiment. Operations 900 may be indicative ofoperations occurring in a source node that is participating in atwo-step DuCo handover.

Operations 900 begin with the source node receiving an event trigger fora combined event (block 905). The event trigger may be a measurementreport received from a UE. The combined event includes a PSCell additionand a role change. The source node sends a combined instruction for thePSCell addition and the role change to a target node (block 907). Thetarget node may be indicated in the measurement report from the UE. Thecombined instruction may be a message including a PSCell additionrequest and a role change indication. The source node adds the targetnode as a PSCell (block 909). The adding of the target node as a PSCellis part of the PSCell adding process. The source node indicates the rolechange to the UE (block 911). Indicating the role change initiates therole change process. As an example, the indication of the role changetakes place during the reconfiguration procedure. As another example,the indication of the role change takes place during the path update.The source node completes the two-step DuCo handover by receiving aPSCell release instruction (block 913) and releasing the PSCell (block915). The PSCell release instruction may be received from the targetnode. Releasing the PSCell may involve releasing or deleting the UEcontext of the UE in the PSCell (the source node).

FIG. 9B illustrates a flow diagram of example operations 950 occurringin a target node participating in a two-step DuCo handover according tothe first example embodiment. Operations 950 may be indicative ofoperations occurring in a target node that is participating in atwo-step DuCo handover.

Operations 950 begin with the target node receiving a combinedinstruction for PSCell addition and role change from the source node(block 955). The combined instruction may be a message including aPSCell addition request and a role change indication. The combinedinstruction for PSCell addition and role change may include a rolechange indication. The target node establishes a UE context for the UE(block 957), thereby performing the PSCell addition. The target nodeperforms the role change (block 959). The target node receives an eventtrigger for the PSCell release (block 961). The event trigger for thePSCell release may be a transmission received from the UE. The targetnode sends a PSCell release instruction to the source node (block 963).

FIG. 10A illustrates a flow diagram of example operations 1000 occurringin a source node participating in a two-step DuCo handover according tothe second example embodiment. Operations 1000 may be indicative ofoperations occurring in a source node that is participating in atwo-step DuCo handover.

Operations 1000 begin with the source node receiving an event triggerfor PSCell addition (block 1 oo ₅). The event trigger may be ameasurement report from the UE. The source node adds the target node asa PSCell (block 1007). The target node may be indicated in themeasurement report. The source node receives an event trigger for acombined event (block 1009). The combined event includes a role changeand a PSCell release. The source node sends a combined instruction forthe role change and the PSCell release to the target node (block ion).The combined instruction may be a message including a role changeindicator and a PSCell release request. The source node indicates therole change to the UE (block 1013). Indicating the role change initiatesthe role change process. As an example, the indication of the rolechange takes place during the reconfiguration procedure. As anotherexample, the indication of the role change takes place during the pathupdate. The source node receives a PSCell release instruction (block1015) and releases the PSCell (block 1017). The PSCell releaseinstruction may be received from the target node. Releasing the PSCellmay involve releasing or deleting the UE context of the UE at the PSCell(the source node).

FIG. 10B illustrates a flow diagram of example operations 1050 occurringin a target node participating in a two-step DuCo handover according tothe second example embodiment. Operations 1050 may be indicative ofoperations occurring in a target node that is participating in atwo-step DuCo handover.

The target node establishes a UE context for the UE (block loss),thereby performing a PSCell addition. The target node receives acombined instruction for the role change and the PSCell release from thesource node (block 1057). The combined instruction for the role changeand the PSCell release may include a role change indication. The targetnode performs the role change (block 1061). The target node sends aPSCell release instruction to the source node (block 1063).

FIG. 11 illustrates a flow diagram of example operations 1100 occurringin a layered PDCP entity of a UE processing received packets during arole change of a DuCo handover. Operations 1100 may be indicative ofoperations occurring in a layered PDCP entity of a UE processingreceived packets during a role change of a DuCo handover.

Operations 1100 begin with the UE applying a first set of PDCP functionsthat are associated with the source node to packets received before theactivation time (block 1105). The first set of PDCP functions associatedwith the source node includes sequence number assignment and headercompression. The UE applies a first set of PDCP functions that areassociated with the target node to packets received after the activationtime (block 1107). The first set of PDCP functions associated with thetarget node includes sequence number assignment and header compression.The UE applies a second set of PDCP functions that are associated withthe source node when communicating with the source node (block 1109).The second set of PDCP functions associated with the source nodeincludes header addition and/or removal and deciphering and/orciphering. The UE applies a second set of PDCP functions that areassociated with the target node when communicating with the target node(block 1111). The second set of PDCP functions associated with thetarget node includes header addition and/or removal and decipheringand/or ciphering.

FIG. 12 illustrates a flow diagram of example operations 1200 occurringin a device processing received PDCP packets. Operations 1200 may beindicative of operations occurring in a device that is processingreceived PDCP packets.

Operations 1200 begin with the device receiving PDCP PDUs (block 1205).The device processes the PDCP PDUs to produce SDUs (block 1207).Processing the PDCP PDUs includes using lower PDCP functions associatedwith an access node with which the device is communicating and upperPDCP functions associated with a PCell of the device. The upper PDCPfunctions include at least sequence number assignment. The device checksthe SDUs against previously produced SDUs for duplicates (block 1209).

FIG. 13 illustrates an example communication system 1300. In general,the system 1300 enables multiple wireless or wired users to transmit andreceive data and other content. The system 1300 may implement one ormore channel access methods, such as code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA(SC-FDMA), or non-orthogonal multiple access (NOMA).

In this example, the communication system 1300 includes electronicdevices (ED) 1310 a-1310 c, radio access networks (RANs) 1320 a-1320 b,a core network 1330, a public switched telephone network (PSTN) 1340,the Internet 1350, and other networks 1360. While certain numbers ofthese components or elements are shown in FIG. 13, any number of thesecomponents or elements may be included in the system 1300.

The EDs 1310 a-1310 c are configured to operate and/or communicate inthe system 1300. For example, the EDs 1310 a-1310 c are configured totransmit and/or receive via wireless or wired communication channels.Each ED 1310 a-1310 c represents any suitable end user device and mayinclude such devices (or may be referred to) as a user equipment/device(UE), wireless transmit/receive unit (WTRU), mobile station, fixed ormobile subscriber unit, cellular telephone, personal digital assistant(PDA), smartphone, laptop, computer, touchpad, wireless sensor, orconsumer electronics device.

The RANs 1320 a-1320 b here include base stations 1370 a-1370 b,respectively. Each base station 1370 a-1370 b is configured towirelessly interface with one or more of the EDs 1310 a-1310 c to enableaccess to the core network 1330, the PSTN 1340, the Internet 1350,and/or the other networks 1360. For example, the base stations 1370a-1370 b may include (or be) one or more of several well-known devices,such as a base transceiver station (BTS), a NodeB (NodeB), an evolvedNodeB (eNodeB), a Home NodeB, a Home eNodeB, a site controller, anaccess point (AP), or a wireless router. The EDs 1310 a-1310 c areconfigured to interface and communicate with the Internet 1350 and mayaccess the core network 1330, the PSTN 1340, and/or the other networks1360.

In the embodiment shown in FIG. 13, the base station 1370 a forms partof the RAN 1320 a, which may include other base stations, elements,and/or devices. Also, the base station 1370 b forms part of the RAN 1320b, which may include other base stations, elements, and/or devices. Eachbase station 1370 a-1370 b operates to transmit and/or receive wirelesssignals within a particular geographic region or area, sometimesreferred to as a “cell.” In some embodiments, multiple-inputmultiple-output (MIMO) technology may be employed having multipletransceivers for each cell.

The base stations 1370 a-1370 b communicate with one or more of the EDs1310 a-1310 c over one or more air interfaces 1390 using wirelesscommunication links. The air interfaces 1390 may utilize any suitableradio access technology.

It is contemplated that the system 1300 may use multiple channel accessfunctionality, including such schemes as described above. In particularembodiments, the base stations and EDs implement LTE, LTE-A, and/orLTE-B. Of course, other multiple access schemes and wireless protocolsmay be utilized.

The RANs 1320 a-1320 b are in communication with the core network 1330to provide the EDs 1310 a-1310 c with voice, data, application, Voiceover Internet Protocol (VoIP), or other services. Understandably, theRANs 1320 a-1320 b and/or the core network 1330 may be in direct orindirect communication with one or more other RANs (not shown). The corenetwork 1330 may also serve as a gateway access for other networks (suchas the PSTN 1340, the Internet 1350, and the other networks 1360). Inaddition, some or all of the EDs 1310 a-1310 c may include functionalityfor communicating with different wireless networks over differentwireless links using different wireless technologies and/or protocols.Instead of wireless communication (or in addition thereto), the EDs maycommunicate via wired communication channels to a service provider orswitch (not shown), and to the Internet 1350.

Although FIG. 13 illustrates one example of a communication system,various changes may be made to FIG. 13. For example, the communicationsystem 1300 could include any number of EDs, base stations, networks, orother components in any suitable configuration.

FIGS. 14A and 14B illustrate example devices that may implement themethods and teachings according to this disclosure. In particular, FIG.14A illustrates an example ED 1410, and FIG. 14B illustrates an examplebase station 1470. These components could be used in the system 1300 orin any other suitable system.

As shown in FIG. 14A, the ED 1410 includes at least one processing unit1400. The processing unit 1400 implements various processing operationsof the ED 1410. For example, the processing unit 1400 could performsignal coding, data processing, power control, input/output processing,or any other functionality enabling the ED 1410 to operate in the system1300. The processing unit 1400 also supports the methods and teachingsdescribed in more detail above. Each processing unit 1400 includes anysuitable processing or computing device configured to perform one ormore operations. Each processing unit 1400 could, for example, include amicroprocessor, microcontroller, digital signal processor, fieldprogrammable gate array, or application specific integrated circuit.

The ED 1410 also includes at least one transceiver 1402. The transceiver1402 is configured to modulate data or other content for transmission byat least one antenna or NIC (Network Interface Controller) 1404. Thetransceiver 1402 is also configured to demodulate data or other contentreceived by the at least one antenna 1404. Each transceiver 1402includes any suitable structure for generating signals for wireless orwired transmission and/or processing signals received wirelessly or bywire. Each antenna 1404 includes any suitable structure for transmittingand/or receiving wireless or wired signals. One or multiple transceivers1402 could be used in the ED 1410, and one or multiple antennas 1404could be used in the ED 1410. Although shown as a single functionalunit, a transceiver 1402 could also be implemented using at least onetransmitter and at least one separate receiver.

The ED 1410 further includes one or more input/output devices 1406 orinterfaces (such as a wired interface to the Internet 1350). Theinput/output devices 1406 facilitate interaction with a user or otherdevices (network communications) in the network. Each input/outputdevice 1406 includes any suitable structure for providing information toor receiving/providing information from a user, such as a speaker,microphone, keypad, keyboard, display, or touch screen, includingnetwork interface communications.

In addition, the ED 1410 includes at least one memory 1408. The memory1408 stores instructions and data used, generated, or collected by theED 1410. For example, the memory 1408 could store software or firmwareinstructions executed by the processing unit(s) 1400 and data used toreduce or eliminate interference in incoming signals. Each memory 1408includes any suitable volatile and/or non-volatile storage and retrievaldevice(s). Any suitable type of memory may be used, such as randomaccess memory (RAM), read only memory (ROM), hard disk, optical disc,subscriber identity module (SIM) card, memory stick, secure digital (SD)memory card, and the like.

As shown in FIG. 14B, the base station 1470 includes at least oneprocessing unit 1450, at least one transceiver 1452, which includesfunctionality for a transmitter and a receiver, one or more antennas1456, at least one memory 1458, and one or more input/output devices orinterfaces 1466. A scheduler, which would be understood by one skilledin the art, is coupled to the processing unit 1450. The scheduler couldbe included within or operated separately from the base station 1470.The processing unit 1450 implements various processing operations of thebase station 1470, such as signal coding, data processing, powercontrol, input/output processing, or any other functionality. Theprocessing unit 1450 can also support the methods and teachingsdescribed in more detail above. Each processing unit 1450 includes anysuitable processing or computing device configured to perform one ormore operations. Each processing unit 1450 could, for example, include amicroprocessor, microcontroller, digital signal processor, fieldprogrammable gate array, or application specific integrated circuit.

Each transceiver 1452 includes any suitable structure for generatingsignals for wireless or wired transmission to one or more EDs or otherdevices. Each transceiver 1452 further includes any suitable structurefor processing signals received wirelessly or by wire from one or moreEDs or other devices. Although shown combined as a transceiver 1452, atransmitter and a receiver could be separate components. Each antenna1456 includes any suitable structure for transmitting and/or receivingwireless or wired signals. While a common antenna 1456 is shown here asbeing coupled to the transceiver 1452, one or more antennas 1456 couldbe coupled to the transceiver(s) 1452, allowing separate antennas 1456to be coupled to the transmitter and the receiver if equipped asseparate components. Each memory 1458 includes any suitable volatileand/or non-volatile storage and retrieval device(s). Each input/outputdevice 1466 facilitates interaction with a user or other devices(network communications) in the network. Each input/output device 1466includes any suitable structure for providing information to orreceiving/providing information from a user, including network interfacecommunications.

FIG. 15 is a block diagram of a computing system 1500 that may be usedfor implementing the devices and methods disclosed herein. For example,the computing system can be any entity of UE, access network (AN),mobility management (MM), session management (SM), user plane gateway(UPGW), and/or access stratum (AS). Specific devices may utilize all ofthe components shown or only a subset of the components, and levels ofintegration may vary from device to device. Furthermore, a device maycontain multiple instances of a component, such as multiple processingunits, processors, memories, transmitters, receivers, etc. The computingsystem 1500 includes a processing unit 1502. The processing unitincludes a central processing unit (CPU) 1514, memory 1508, and mayfurther include a mass storage device 1504, a video adapter 1510, and anI/O interface 1512 connected to a bus 1520.

The bus 1520 may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, or avideo bus. The CPU 1514 may comprise any type of electronic dataprocessor. The memory 1508 may comprise any type of non-transitorysystem memory such as static random access memory (SRAM), dynamic randomaccess memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM),or a combination thereof. In an embodiment, the memory 1508 may includeROM for use at boot-up, and DRAM for program and data storage for usewhile executing programs.

The mass storage 1504 may comprise any type of non-transitory storagedevice configured to store data, programs, and other information and tomake the data, programs, and other information accessible via the bus1520. The mass storage 1504 may comprise, for example, one or more of asolid state drive, hard disk drive, a magnetic disk drive, or an opticaldisk drive.

The video adapter 1510 and the I/O interface 1512 provide interfaces tocouple external input and output devices to the processing unit 1502. Asillustrated, examples of input and output devices include a display 1518coupled to the video adapter 1510 and a mouse/keyboard/printer 1516coupled to the I/O interface 1512. Other devices may be coupled to theprocessing unit 1502, and additional or fewer interface cards may beutilized. For example, a serial interface such as Universal Serial Bus(USB) (not shown) may be used to provide an interface for an externaldevice.

The processing unit 1502 also includes one or more network interfaces1506, which may comprise wired links, such as an Ethernet cable, and/orwireless links to access nodes or different networks. The networkinterfaces 1506 allow the processing unit 1502 to communicate withremote units via the networks. For example, the network interfaces 1506may provide wireless communication via one or more transmitters/transmitantennas and one or more receivers/receive antennas. In an embodiment,the processing unit 1502 is coupled to a local-area network 1522 or awide-area network for data processing and communications with remotedevices, such as other processing units, the Internet, or remote storagefacilities.

It should be appreciated that one or more steps of the embodimentmethods provided herein may be performed by corresponding units ormodules. For example, a signal may be transmitted by a transmitting unitor a transmitting module. A signal may be received by a receiving unitor a receiving module. A signal may be processed by a processing unit ora processing module. Other steps may be performed by an addingunit/module, an indicating unit/module, a releasing unit/module, aforwarding unit/module, an establishing unit/module, an operatingunit/module, an applying unit/module, a processing unit/module, achecking unit/module, and/or a changing unit/module. The respectiveunits/modules may be hardware, software, or a combination thereof. Forinstance, one or more of the units/modules may be an integrated circuit,such as field programmable gate arrays (FPGAs) or application-specificintegrated circuits (ASICs).

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims.

What is claimed is:
 1. A method for processing packets during a rolechange between a first access node and a second access node, the methodcomprising: processing, by a user equipment (UE), a first set ofpackets, using a first set of packet data convergence protocol (PDCP)functions associated with the first access node prior to a processing ofa switch indicator, wherein the first set of PDCP functions associatedwith the first access node includes sequence number assignment andheader compression, and wherein the switch indicator indicates the rolechange; processing, by the UE, a second set of packets, using a secondset of PDCP functions associated with the second access node after theprocessing of the switch indicator, wherein the second set of PDCPfunctions associated with the second access node includes sequencenumber assignment and header compression; processing, by the UE, a thirdset of packets, using a third set of PDCP functions associated with thefirst access node when communicating with the first access node, whereinthe third set of PDCP functions associated with the first access nodeincludes header addition and/or removal and deciphering and/orciphering; and processing, by the UE, a fourth set of packets, using afourth set of PDCP functions associated with the second access node whencommunicating with the second access node, wherein the fourth set ofPDCP functions associated with the second access node includes headeraddition and/or removal and deciphering and/or ciphering.
 2. The methodof claim 1, wherein the switch indicator is an activation time, andwherein processing the third set of PDCP functions associated with thefirst access node and processing the fourth set of PDCP functionsassociated with the second access node occur both prior to andsubsequent to the activation time.
 3. The method of claim 2, wherein theactivation time comprises a time when the role change occurs.
 4. Themethod of claim 2, further comprising: exchanging, by the UE with thefirst access node, the first set of packets prior to the activationtime; and exchanging, by the UE with the first access node, the thirdset of packets when communicating with the first access node.
 5. Themethod of claim 2, further comprising: exchanging, by the UE with thesecond access node, the second set of packets after the activation time;and exchanging, by the UE with the second access node, the fourth set ofpackets when communicating with the second access node.
 6. The method ofclaim 1, wherein the switch indicator is a PDCP protocol data unit (PDU)indicating the role change, and wherein processing the third set of PDCPfunctions associated with the first access node and processing thefourth set of PDCP functions associated with the second access nodeoccur both prior to and subsequent to the processing of the PDCP PDU. 7.The method of claim 6, further comprising: exchanging, by the UE withthe first access node, the first set of packets prior to the processingof the PDCP PDU; and exchanging, by the UE with the first access node,the third set of packets when communicating with the first access node.8. The method of claim 6, further comprising: exchanging, by the UE withthe second access node, the second set of packets after the processingof the PDCP PDU; and exchanging, by the UE with the second access node,the fourth set of packets when communicating with the second accessnode.
 9. The method of claim 6, wherein the PDCP PDU is a PDCP controlPDU indicating the role change or a PDCP data PDU including an endmarker.
 10. The method of claim 1, further comprising: sending, by theUE to the first access node, an event trigger for a combined event, theevent trigger triggering the role change.
 11. The method of claim 10,wherein the event trigger reflects a combination of a first qualityindicator associated with the first access node falling below a firstthreshold and a second quality indicator associated with the secondaccess node rising above a second threshold relative to a third qualityindicator associated with the first access node.
 12. An apparatuscomprising: a non-transitory memory storage comprising instructions; andone or more processors in communication with the non-transitory memorystorage, wherein the one or more processors execute, during a rolechange between a first access node and a second access node, theinstructions to: process a first set of packets, using a first set ofpacket data convergence protocol (PDCP) functions associated with thefirst access node prior to a processing of a switch indicator, whereinthe first set of PDCP functions associated with the first access nodeincludes sequence number assignment and header compression, and whereinthe switch indicator indicates the role change; process a second set ofpackets, using a second set of PDCP functions associated with the secondaccess node after the processing of the switch indicator, wherein thesecond set of PDCP functions associated with the second access nodeincludes sequence number assignment and header compression; process athird set of packets, using a third set of PDCP functions associatedwith the first access node when communicating with the first accessnode, wherein the third set of PDCP functions associated with the firstaccess node includes header addition and/or removal and decipheringand/or ciphering; and process a fourth set of packets, using a fourthset of PDCP functions associated with the second access node whencommunicating with the second access node, wherein the fourth set ofPDCP functions associated with the second access node includes headeraddition and/or removal and deciphering and/or ciphering.
 13. Theapparatus of claim 12, wherein the switch indicator is an activationtime, and wherein processing the third set of PDCP functions associatedwith the first access node and processing the fourth set of PDCPfunctions associated with the second access node occur both prior to andsubsequent to the activation time.
 14. The apparatus of claim 13,wherein the activation time comprises a time when the role changeoccurs.
 15. The apparatus of claim 13, wherein the one or moreprocessors execute the instructions further to: exchange, with the firstaccess node, the first set of packets prior to the activation time; andexchange, with the first access node, the third set of packets whencommunicating with the first access node.
 16. The apparatus of claim 13,wherein the one or more processors execute the instructions further to:exchange, with the second access node, the second set of packets afterthe activation time; and exchange, with the second access node, thefourth set of packets when communicating with the second access node.17. The apparatus of claim 12, wherein the switch indicator is a PDCPprotocol data unit (PDU) indicating the role change, and whereinprocessing the third set of PDCP functions associated with the firstaccess node and processing the fourth set of PDCP functions associatedwith the second access node occur both prior to and subsequent to theprocessing of the PDCP PDU.
 18. The apparatus of claim 17, wherein theone or more processors execute the instructions further to: exchange,with the first access node, the first set of packets prior to theprocessing of the PDCP PDU; and exchange, with the first access node,the third set of packets when communicating with the first access node.19. The apparatus of claim 17, wherein the one or more processorsexecute the instructions further to: exchange, with the second accessnode, the second set of packets after the processing of the PDCP PDU;and exchange, with the second access node, the fourth set of packetswhen communicating with the second access node.
 20. The apparatus ofclaim 17, wherein the PDCP PDU is a PDCP control PDU indicating the rolechange or a PDCP data PDU including an end marker.